1. Field of the Invention
The invention relates to circuit interrupters and, more particularly, to circuit breakers with mechanisms that trip the circuit breaker when voltage in the protected circuit drops below a specified value. The invention also relates to handle arms used in such mechanisms.
2. Background Information
Circuit interrupters, such as, for example, circuit breakers, primarily provide protection from excessive current in an electric power distribution system. Some circuit breakers additionally provide protection against low voltage that could damage or cause misoperation of equipment in the protected circuit. Typically, low voltage protection is provided by an undervoltage release (UVR) that includes a coil energized by the protected circuit. As long as the voltage remains above a predetermined dropout level, the magnetic force generated by the coil is sufficient to maintain a plunger in a retracted position. However, when the voltage drops below the predetermined dropout level, a compression spring overcomes the magnetic force and extends the plunger out of the coil to actuate the trip mechanism of the circuit breaker. The magnetic force generated by the coil is not sufficient to retract the plunger against the bias of the compression spring even if it returns to full value. Consequently, a reset lever is provided to mechanically retract the plunger.
It is known to actuate the reset lever when the handle of the circuit breaker is returned to the off position, such as shown in U.S. Pat. No. 7,369,021. Such resetting has been accomplished by the interaction of a pin member, separately added to the handle arm, and a reset lever on the overvoltage relay as the handle arm reaches the off position.
While such reset design is effective, there is room for improvement in undervoltage release mechanisms for circuit interrupters. There is also room for improvement in the structure of the mechanisms that reset such release mechanisms and circuit interrupters employing such undervoltage release mechanisms.